{"id":"f49b3340-4225-465a-aa49-ffec6d4523bf","arxiv_id":"2507.07866","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":7,"one_line_summary":"Cooling a 100 nm YBCO film through Tc increases visible transmittance by roughly 35-40% and decreases reflectance, with wavelength-dependent magnitude; the authors model the effect with a two-fluid picture.","lead":"Thin films of the superconductor YBCO let more visible light through and reflect less as they cool through their superconducting transition, with the effect strongest near 633 nm. The paper suggests these color-dependent changes could be used as a non-contact way to find a film's critical temperature.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"No non-superconducting YBCO control or STO control at 450-580 nm was measured; the 35-41% transmittance rise and 76% reflectance drop could be normal-state temperature effects, so the optical-Tc link is not yet established.","rationale":"The reader's weakest_assumption already identifies the substrate control gap at shorter wavelengths and the oxygen-content drift. I agree with both, but the most load-bearing element is the complete absence of a non-superconducting YBCO control: no experiment rules out temperature-dependent normal-state optical properties of the film itself (e.g., carrier scattering, oxygen ordering, thermoreflectance) as the source of the large 633-nm reflectance drop and the 35-41% transmittance increases. The reader's proposed checks (extend substrate control, remeasure EDS/Tc) would strengthen the substrate and stoichiometry legs, but would still not separate the superconducting transition from normal-state film optics. A Tc < 10 K YBCO film is the decisive control. I also note an internal inconsistency in the wavelength dependence: Table I lists maximum change 41% at 580 nm and 39% at 630 nm, while the abstract states the maximum is at 633 nm; this weakens the empirical basis for the β(ℏω) model in Section IV, but it is secondary to the missing control. Because the central claim is otherwise plausible and testable, the existing CONDITIONAL verdict remains appropriate; no verdict change is recommended.","tokens_in":8918,"tokens_out":8285,"duration_ms":89274,"concrete_test":"Measure transmittance and reflectance versus temperature (10-300 K) with the same optical setup on: (1) a bare STO substrate at 450, 500, 530, 580, and 630 nm, and (2) an oxygen-depleted YBCO film on STO with Tc < 10 K (same 100 nm thickness and mounting) at the same wavelengths. If either control reproduces a >=35% relative transmittance increase or the 633-nm reflectance drop in the 70-100 K window, the superconducting attribution fails; if both are flat, the claim is supported. Additionally, remeasure EDS and resistive Tc after the optical runs to rule out oxygen drift.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim, that the transmittance and reflectance changes near Tc are caused by the superconducting transition, rests on two under-tested assumptions. First, the bare-STO control (Fig. 6) was measured only at 633 nm, yet the wavelength-dependent claims (Fig. 8, Table I) extend from 450 nm to 630 nm. Near its band edge (~380 nm), STO's extinction coefficient and refractive index can be temperature dependent, and even a small Δn shifts Fabry-Perot fringes in the 0.5 mm substrate, potentially producing apparent transmittance changes of the observed magnitude. Second, and more decisive, the YBCO film's own normal-state optical constants were never controlled for: a 100 nm film on STO was measured only in its superconducting state, and Section IIB reports that prior vacuum cycles reduced oxygen content from 6.84 to 5.83, with no post-anneal EDS or post-run Tc verification reported. The 76% reflectance drop at 633 nm is far larger than expected from the two-fluid model's visible-frequency Drude tail, and could arise from temperature-dependent normal-state scattering, oxygen reordering, or thermoreflectance. The logistic-fit midpoints (82-88 K, Table II) overlapping resistive Tc (87±3 K) are necessary but not sufficient; any broad monotonic optical change in this temperature window would produce a similar midpoint. Without a non-superconducting YBCO control (e.g., Tc < 10 K) or substrate controls at all measured wavelengths, the correlation is not identified as superconducting in origin.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports temperature-dependent transmittance and reflectance measurements of a 100 nm YBCO thin film on an STO substrate, covering 450 nm to 633 nm and temperatures from about 12 K to 300 K. The central observation is an increase in transmittance and a decrease in reflectance as the sample is cooled through the superconducting transition, with the optical change saturating a few kelvins below Tc. Logistic fits to the optical transmittance at several wavelengths give midpoint temperatures of 82-88 K, consistent with the resistive Tc of 87 ± 3 K. The authors propose a two-fluid model in which a photon-energy-dependent factor beta(hbar omega) depletes the superconducting fluid, yielding a qualitative account of the wavelength-dependent transmittance increase. The paper claims a non-contact optical route to determining Tc in high-Tc thin films.","tokens_in":9316,"tokens_out":2845,"duration_ms":35737,"significance":"If the observed optical changes are genuinely tied to the superconducting transition, the result would be useful for non-contact Tc diagnostics in thin-film superconductors, particularly for samples where electrical contacts are impractical. The manuscript has several strengths: simultaneous electrical and optical measurements on the same film, a substrate-only control at 633 nm, reproducibility between the 633 nm and 630 nm runs, and an explicit attempt to model the wavelength dependence. However, the significance is conditional on controls that are currently missing: the substrate control is not repeated at the other measured wavelengths, no non-superconducting YBCO or otherwise normal-state film is measured, and the film's oxygen content and Tc are not re-verified after the annealing step. The model also contains a hand-inserted wavelength dependence, so agreement with the data is partly circular. These gaps mean the central attribution to superconductivity is not yet established.","major_comments":[{"comment":"The film's history undermines the attribution of the optical change to the superconducting transition. The manuscript reports that prior vacuum cycles reduced the oxygen content from YBa2Cu3O6.84 to YBa2Cu3O5.83 and that this reduced Tc, and that the sample was subsequently annealed in O2. However, no post-anneal EDS or post-run Tc verification is reported, so there is no direct evidence that the film measured in the optical runs was in the superconducting state with the claimed stoichiometry. Without this verification, temperature-dependent optical changes could reflect oxygen reordering or normal-state effects rather than the superconducting transition.","section":"Section IIB and Fig. 2 caption"},{"comment":"The substrate control is insufficient for the wavelength-dependent claims. The refractive-index-vs-temperature measurement of bare STO was performed only at 633 nm, yet Table I and Fig. 8 present transmittance changes at 450, 500, 530, 580, and 630 nm. STO has a band edge near 380 nm, and its refractive index and extinction coefficient can be temperature dependent at shorter wavelengths; even a small change in n would shift Fabry-Perot fringes in the 0.5 mm substrate and could mimic transmittance changes of the observed magnitude. A bare-STO control at each measured wavelength, or an estimate of the substrate-induced uncertainty, is required to support the claim that the changes are intrinsic to the YBCO film.","section":"Section IIIC and Fig. 6"},{"comment":"The model's wavelength dependence is inserted by hand, so the model's agreement with Table I is circular. The factor beta(hbar omega) = 1 - exp(-Egap / (kappa hbar omega)) in Eq. (6) is introduced specifically to make the superconducting fluid depletion depend on photon energy, and its parameters Egap and kappa are not independently determined. Likewise gamma, tau(Tc), alpha, lambda_L(0), n0, and mn are free or taken from unspecified sources. Consequently, the model does not independently predict the observed wavelength dependence; it restates the input. The authors acknowledge the model is qualitative, but the text should explicitly distinguish the fitted/inserted wavelength dependence from a predictive two-fluid derivation.","section":"Section IV, Eqs. (5)-(6)"},{"comment":"The reported 76% decrease in reflectance at 633 nm is surprisingly large for a visible-frequency two-fluid effect, since the condensate's Drude-like contribution at these photon energies is expected to be small. The manuscript does not measure the normal-state optical constants of the same film above Tc in a controlled way, nor does it provide a non-superconducting YBCO control (for example, an oxygen-deficient film with Tc below 10 K). As a result, the observed reflectance drop could also arise from temperature-dependent normal-state scattering, thermoreflectance, or stress-induced changes. The logistic-fit midpoint overlapping the resistive Tc is necessary but not sufficient, because any broad monotonic optical change in the same temperature window would produce a similar midpoint.","section":"Section IIIB and Fig. 5"}],"minor_comments":[{"comment":"There is a typo in the third paragraph: 'weas' should be 'was'.","section":"Section IIA"},{"comment":"The section heading reads 'DISICUSSION'; it should be 'DISCUSSION'.","section":"Section IV heading"},{"comment":"The furnace manufacturer is spelled 'Linberg' in the text; the usual spelling is 'Lindberg'.","section":"Section IIB"},{"comment":"The abstract and text state that the minimum transmittance change occurs at 450 nm, but Table I lists 36 ± 2% at 450 nm and 35 ± 2% at 500 nm. Within the stated uncertainties the values are equal, and the claim of a monotonic wavelength trend should be softened or reworded.","section":"Table I and Abstract"},{"comment":"The light sources are described as 'mixed polarized' without specifying the polarization state or its stability; since reflectance measurements are polarization sensitive, the manuscript should clarify how polarization affects the near-normal-incidence reflectance data.","section":"Section IIA and IIIB"},{"comment":"The beam-splitter correction fractions are stated to be valid specifically for 633 nm, but the variable-wavelength transmittance measurements in Section IIIC use only the window correction. The manuscript should either provide the beam-splitter wavelength dependence or explicitly justify why it does not enter the transmittance calculation at other wavelengths.","section":"Fig. 3 and Section IIIC"}],"recommendation":"major_revision","confidential_remarks":"The manuscript addresses a topical and potentially useful diagnostic, but in its current form the central claim is not fully supported by the evidence. The missing controls (multi-wavelength substrate runs, a non-superconducting comparison film, and post-anneal stoichiometry/Tc verification) are experimentally feasible and would substantially strengthen the paper. The model section should be reframed to make clear which elements are fitted rather than predictive. I would be willing to review a revised version."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Things you should know about arXiv:2507.07866. It is a straightforward optical spectroscopy study of one 100 nm YBCO film on STO. The genuinely new part is the multiwavelength transmittance data (450–630 nm) as a function of temperature across the superconducting transition, with a quoted 35–41% increase in transmittance and a large relative reflectance drop at 633 nm. That dataset is absent from the earlier literature, where Fishman et al. used differential reflectance at 780 nm and Lai and Lue measured reflectance/dielectric functions. As a measurement, it is a legitimate extension.\n\nWhat the paper does well: the cryostat records reflectance, transmittance, and resistivity simultaneously; the optical correction factors are spelled out; the 630 nm run reproduces the 633 nm result; and a bare STO substrate measured at 633 nm shows no significant temperature dependence in its refractive index. The logistic-fit midpoints (82–88 K) overlap the resistive Tc (87±3 K), which is consistent.\n\nNow the soft spots, in order of severity. First, the experiment does not isolate superconductivity. The STO control is only at 633 nm, while the wavelength-dependent claims go down to 450 nm; that is a gap, though STO is fairly inert in this range. More importantly, there is no non-superconducting YBCO control, and the film's oxygen content after the oxygen annealing is not verified by EDS, nor is Tc re-measured after the later optical runs (the paper states that earlier vacuum cycles had reduced O from 6.84 to 5.83). The 76% reflectance drop is far larger than the two-fluid model would suggest in the visible, so a normal-state thermoreflectance artifact is a live possibility. Second, the model is not a test: the wavelength dependence is inserted by hand through β(ℏω) in Eqs. (5)–(6), the parameters have no independent values, and the model curves are not overlaid on the data. Third, there is an internal inconsistency: Section IV says the transmittance change at 450 nm is about half that at 630 nm, while Table I lists 36% versus 39%. That needs to be cleaned up.\n\nWho is this for? People looking for non-contact Tc diagnostics or optical readout of superconducting devices. It is a moderate, useful result, not a breakthrough. A serious referee should see it, but with a clear request for added controls, post-anneal characterization, and a quantitative model comparison. My recommendation: send it to peer review and expect heavy revision.","headline":"New multiwavelength transmittance data on YBCO through Tc, but the superconducting origin of the signal is not yet nailed down; deserves peer review with major revision.","tokens_in":9887,"tokens_out":8744,"would_cite":false,"duration_ms":80753,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Visible light detects the superconducting transition of a 100 nm YBCO film: transmittance rises 35-41% as the film cools through its critical temperature.","keywords":["YBCO thin films","high-temperature superconductors","optical transmittance","two-fluid model","critical temperature measurement","cryogenic optical spectroscopy","non-contact Tc readout","visible spectroscopy"],"falsifier":"Repeat the wavelength-dependent transmittance sweeps on a bare strontium titanate substrate and on an oxygen-depleted YBCO film with no superconducting transition; if either shows a comparable 35-41% transmittance rise between 100 K and 70 K, the optical signal is not uniquely tied to superconductivity.","tokens_in":8709,"feed_emoji":"🔬","tokens_out":8584,"duration_ms":90945,"temperature":0.7,"pith_summary":"The paper tries to establish that the superconducting transition of a high-temperature superconductor can be seen in ordinary visible light without electrical contacts. Cooling a 100 nm YBCO film on strontium titanate raises its transmittance by 35-41% relative to room temperature and lowers its reflectance, with the change starting near 100 K and saturating near 70 K. Logistic midpoints of the transmittance curves give optical Tc values of 80-88 K, consistent with the 87±3 K obtained from resistivity. If correct, this makes transmittance a practical non-contact thermometer for Tc in thin films, and a two-fluid model with a photon-coupling term accounts for the observed wavelength dependence.","feed_headline":"Cooling YBCO through Tc boosts transparency by 41%","feed_subtitle":"Visible-light transmittance midpoints match resistive Tc in a 100 nm film, enabling contact-free Tc readout.","key_machinery":"The argument is carried by the two-fluid dielectric response of the film: charge carriers are split into a normal-fluid density $n_n$ and a condensate density $n_s$, and the effective permittivity is written so that absorption enters through $n_n(T,\\hbar\\omega)$. The paper adapts an empirical microwave-frequency permittivity model by removing microwave-specific approximations and adding a coupling factor $\\beta(\\hbar\\omega)=1-e^{-E_{\\rm gap}/\\kappa\\hbar\\omega}$, which weakens the condensate's contribution when photon energy grows. The resulting complex refractive index is put into multilayer transmittance equations to produce the predicted transmittance-versus-temperature curves. On the data side, the load-bearing operation is a logistic fit to the transmittance and reflectance curves whose midpoint defines the optical Tc.","core_discovery":"The central claim is that 100 nm epitaxial YBCO films show a reproducible, wavelength-dependent optical response tied to the superconducting transition. At 633 nm, transmittance increases by up to 37% and reflectance falls by up to 76% while cooling through the transition; across 450-630 nm the transmittance change is 35-41%, largest near 580-633 nm and smallest at 450 nm. The midpoint of a logistic fit to transmittance gives Tc estimates between 80 and 88 K, while the resistivity midpoint is 87±3 K. The authors interpret the effect as the superconducting condensate reducing optical absorption, and a two-fluid model modified so that photons can convert some condensate back into normal carriers reproduces the temperature and wavelength trends. They conclude that the same optical signal could be used as a non-contact measurement of Tc in high-Tc thin films.","pith_inferences":["Beyond the paper, the same transmittance jump could be used to map Tc homogeneity across a film by imaging rather than spot-measuring, since the effect saturates within a few kelvins.","The paper's beta coupling predicts that the optical change should weaken as photon energy grows beyond the gap; measuring at shorter wavelengths would test whether the 35% floor at 450 nm becomes a sharp cutoff.","If the effect is confirmed, a single temperature-stabilized comparison above and below Tc could act as a fast optical superconducting-or-not readout, which would fit naturally into detector or sensor applications."],"forward_implications":["A non-contact optical measurement can determine Tc of a high-Tc thin film from transmittance alone, with midpoint values between 80 and 88 K that agree with resistivity.","The optical transition begins near 100 K and saturates within a few kelvins below Tc, giving a sharp, reproducible optical fingerprint of the superconducting state in the visible band.","The magnitude of the transmittance change is wavelength dependent, largest near 580-633 nm and smallest near 450 nm, so the effect is not a simple broadband transparency change.","A two-fluid model with a photon-coupling term reproduces the temperature and wavelength dependence qualitatively, providing a physical story for why visible light can sense the transition.","Reflectance and transmittance both track the same transition, giving two independent optical handles on Tc."],"supporting_citations":[{"why":"This reference demonstrates that differential optical reflectance of YBCO at 780 nm has a sharp peak at Tc, providing the precedent for optical Tc measurement.","marker":"[14]"},{"why":"This reference supplies the commercial 100 nm YBCO-on-STO film used in the experiment, including the vendor Tc specification.","marker":"[15]"},{"why":"This reference presents the two-fluid model of superconductivity that the paper adapts to visible frequencies.","marker":"[16]"},{"why":"This reference provides the empirical microwave permittivity model whose assumptions the paper removes and extends with a photon-coupling term.","marker":"[17]"},{"why":"This reference applies the two-fluid model to YBCO transmission in the millimeter regime, supporting its use for transmission changes.","marker":"[20]"},{"why":"This reference supplies the multilayer transmittance equations used to convert the modeled permittivity into temperature-dependent transmittance.","marker":"[21]"}],"fun_headline_variants":["YBCO films turn clearer at superconducting transition","Optical probe detects Tc in YBCO thin films","Transmittance spikes mark YBCO superconductivity","Visible light reveals YBCO superconducting phase","YBCO transparency change signals Tc onset"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The claims stand on the assumption that the rise in transmittance and fall in reflectance between about 100 K and 70 K come from the YBCO film entering the superconducting state, not from temperature-dependent changes in the substrate, the optical windows, or the film's oxygen content.","fun_headline_variants_meta":{"raw":{"variants":["YBCO films turn clearer at superconducting transition","Optical probe detects Tc in YBCO thin films","Transmittance spikes mark YBCO superconductivity","Visible light reveals YBCO superconducting phase","YBCO transparency change signals Tc onset"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000181,"raw_usage":{"total_tokens":1288,"prompt_tokens":910,"completion_tokens":378,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":526,"completion_tokens_details":{"reasoning_tokens":308}},"tokens_in":526,"tokens_out":378,"duration_ms":4781,"temperature":1.0,"reasoning_tokens":308,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T18:31:35.727203+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Repeat the wavelength-dependent transmittance sweeps on a bare strontium titanate substrate and on an oxygen-depleted YBCO film with no superconducting transition; if either shows a comparable 35-41% transmittance rise between 100 K and 70 K, the optical signal is not uniquely tied to superconductivity.","supporting_citations":[{"cited_title":"Fishman, W","cited_arxiv_id":null,"evidence_quote":"This reference demonstrates that differential optical reflectance of YBCO at 780 nm has a sharp peak at Tc, providing the precedent for optical Tc measurement."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"This reference supplies the commercial 100 nm YBCO-on-STO film used in the experiment, including the vendor Tc specification."},{"cited_title":"Vendik, I","cited_arxiv_id":null,"evidence_quote":"This reference provides the empirical microwave permittivity model whose assumptions the paper removes and extends with a photon-coupling term."},{"cited_title":"Tsiatmas, A","cited_arxiv_id":null,"evidence_quote":"This reference applies the two-fluid model to YBCO transmission in the millimeter regime, supporting its use for transmission changes."},{"cited_title":"Swanepoel, Determination of the thickness and optical constants of amorphous silicon, J","cited_arxiv_id":null,"evidence_quote":"This reference supplies the multilayer transmittance equations used to convert the modeled permittivity into temperature-dependent transmittance."}],"review_version":1}